Method and apparatus for aligning a laser diode on a slider

ABSTRACT

A structure includes a channel waveguide and a pocket adjacent to an input facet of the channel waveguide. A laser having an output facet is positioned in the pocket. The structure includes a stop on either the laser or a wall of the pocket. The stop is positioned at an interface between the laser and the wall of the pocket such that the output facet of the laser and the input facet of the waveguide are separated by a gap.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/097,710, filed Apr. 29, 2011, which claims the benefit of U.S.Provisional Application Ser. No. 61/330,067, filed Apr. 30, 2010, thecontent of which is incorporated herein by reference in theirentireties.

BACKGROUND

Heat assisted magnetic recording (HAMR) generally refers to the conceptof locally heating a recording media to reduce the coercivity of themedia so that an applied magnetic writing field can more easily directthe magnetization of the media during the temporary magnetic softeningof the media caused by the heat source. A tightly confined, high powerlaser light spot can be used to heat a portion of the recording media.Then the heated portion is subjected to a magnetic field that sets thedirection of magnetization of the heated portion. With HAMR, thecoercivity of the media at ambient temperature can be much higher thanthe coercivity during recording, thereby enabling stability of therecorded bits at much higher storage densities and with much smaller bitcells.

One approach for directing light onto recording media uses a laser diodemounted on a read/write head (also referred to as a “slider”). The laserdiode directs light to a planar waveguide that transmits the light to asmall spot adjacent to an air bearing surface of the slider. Anear-field transducer (NFT) can be included to further concentrate thelight. The near-field transducer is designed to reach a local surfaceplasmon (LSP) condition at a designated light wavelength. At LSP, a highfield surrounding the near-field transducer appears, due to collectiveoscillation of electrons in the metal. Part of the field will tunnelinto an adjacent media and get absorbed, raising the temperature of themedia locally for recording.

A significant consideration for heat assisted magnetic recording (HAMR)is the location of a laser diode that is used as the optical powersource. One current design places a laser diode on the top of a slider.Radiation from the laser diode is focused and directed to couplinggrating on the waveguide using external optical elements. This methodinvolves the development of the external optical elements and could beimplemented by assembling the sliders one-by-one and using activealignment.

A potential embodiment integrates a laser diode into the trailing edgeof the slider and uses a waveguide coupler to guide the laser to thenear field transducer using a combination of light-positioning elementssuch as solid immersion mirrors (SIMs) an/or channel waveguides. Properalignment between the laser diode and the waveguide is needed to achievethe desired coupling of light from the laser to the waveguide. Inaddition, this needs to be accomplished in a cost-effective manner.

SUMMARY

In one aspect, an apparatus includes: a structure including a channelwaveguide and a pocket adjacent to an input facet of the channelwaveguide; a laser having an output facet and being positioned in thepocket; and a stop on at least one of the laser and a wall of thepocket; wherein the stop is positioned at an interface between the laserand the wall of the pocket such that the output facet of the laser andthe input facet of the waveguide are separated by a gap.

In another aspect, a method involves: providing a structure including achannel waveguide and a pocket adjacent to an input facet of the channelwaveguide; positioning a laser having an output facet in the pocket;forcing the laser toward a wall of the pocket until an axial stop on atleast one of the laser and the wall of the pocket is positioned at aninterface between the laser and the wall of the pocket such that theoutput facet of the laser and the input facet of the waveguide areseparated by a gap; and fixing the relative position of the laser andthe channel waveguide.

In another aspect, a method involves: positioning a carrier waferrelative to a head wafer such that each of a plurality of laser diodesof the carrier wafer is aligned with an alignment feature of acorresponding one of a plurality of slider portions of the head wafer;injecting a gas between the carrier wafer and the head wafer viaopenings in at least one the carrier wafer and the head wafer to createpreferential surface conditions on solder surfaces therebetween; andperforming a reflow operation to bond the laser diodes to thecorresponding slider portions, wherein the reflow operation furthercauses a final alignment therebetween in cooperation with the alignmentfeatures of the slider portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation of a data storage device in theform of a disc drive that can include a slider in accordance with anembodiment.

FIG. 2 is a cross-sectional view of a laser diode and a portion of aslider.

FIG. 3 is an isometric view of a laser diode and a portion of a slider.

FIG. 4 is a cross-sectional view of a laser diode and a portion of aslider.

FIG. 5 is a cross-sectional view of a laser diode and a portion of aslider.

FIG. 6 is a cross-sectional view of a laser diode and a portion of aslider.

FIG. 7 is an isometric view of a portion of the pocket in the slider.

FIG. 8 is a cross-sectional view of a portion of the pocket in theslider, including bonding pads.

FIG. 9 is a cross-sectional view of a portion of the pocket in a slider,including bonding bumps.

FIG. 10 is a cross-sectional view of a laser diode and a portion of aslider.

FIG. 11 is a cross-sectional view of a laser diode and a portion of aslider.

FIG. 12 is a cross-sectional view of a laser diode and a portion of aslider.

FIG. 13 is a cross-sectional view of a first wafer including a pluralityof laser diodes and second wafer including a plurality of sliders.

FIG. 14 is a cross-sectional view of a first wafer including a pluralityof laser diodes and second wafer including a plurality of sliders.

FIG. 15 is a cross-sectional view of a first wafer including a pluralityof laser diodes and second wafer including a plurality of sliders.

FIG. 16 is a perspective view of a laser diode according to an exampleembodiment.

FIG. 17 is a flowchart illustrating assembly of a laser diode to aslider according to an example embodiment.

DETAILED DESCRIPTION

FIG. 1 is a pictorial representation of a data storage device in theform of a disc drive 10 that can include a slider constructed inaccordance with an embodiment. The disc drive 10 includes a housing 12(with the upper portion removed and the lower portion visible in thisview) sized and configured to contain the various components of the discdrive. The disc drive 10 includes a spindle motor 14 for rotating atleast one magnetic storage media 16 within the housing. At least one arm18 is contained within the housing 12, with each arm 18 having a firstend 20 with a recording head or slider 22, and a second end 24 pivotallymounted on a shaft by a bearing 26. An actuator motor 28 is located atthe arm's second end 24 for pivoting the arm 18 to position therecording head 22 over a desired track 27 of the disc 16. The actuatormotor 28 is regulated by a controller, which is not shown in this viewand is well-known in the art.

For heat assisted magnetic recording (HAMR), electromagnetic radiation,for example, visible, infrared or ultraviolet light is directed onto asurface of the recording media to raise the temperature of a localizedarea of the media to facilitate switching of the magnetization of theheated area. Recent designs of HAMR recording heads include a thin filmwaveguide on a slider to guide light to the recording media forlocalized heating of the recording media. A near-field transducerpositioned at the air bearing surface of a recording head can be used todirect the electromagnetic radiation to a small spot on the recordingmedia.

In a HAMR storage device constructed according to one embodiment, alaser diode chip is positioned on the slider. Precise alignment of thelaser diode output and the waveguide is achieved by using laser diodebeds (also referred to as cavities or pockets) with specially designedfeatures, such as stoppers and steps.

FIG. 2 is a cross-sectional view of an example of a slider for use inheat assisted magnetic recording. The slider 30 includes a substrate 32,a base coat 34 on the substrate, waveguide 36 on the base coat, and awrite pole 38 that is positioned adjacent to the waveguide. A coil 40includes conductors that pass around the write pole. A laser diode 42 ispositioned on the slider to direct light onto an input facet 44 of thewaveguide. The light then passes through the waveguide and is used toheat a portion 46 of a storage media 48 that is positioned adjacent toan air bearing surface 50 of the slider. The light may be used with anear field transducer to further control the thermal effects. It isdesirable to align an output facet 52 of the laser diode with the inputfacet of the waveguide to achieve efficient coupling of the light fromthe laser diode to the waveguide. In addition, physical contact betweenthe output facet 52 of the laser diode with the input facet of thewaveguide is to be avoided to prevent damage to the facets that mightoccur from such contact.

In one aspect, a method for alignment of the laser diode and thewaveguide on the slider for Heat Assisted Magnetic Recording (HAMR). Theslider includes geometrical features for passive alignment of a laserdiode and the channel waveguide when the laser diode is placed on theslider.

FIG. 3 shows an example of a portion of a slider 60 having a pocket 62(also called a bed or cavity) with front facet stops 64 and 66. Theslider includes a planar waveguide portion 68 having an input facet 70adjacent to the pocket. The input facet is in a recess 72 in a wall 74of the pocket, with stops 64 and 66 on opposite sides of the recess. Alaser diode 76, which can be in the form of a laser chip, includes anoutput facet 78 from which the laser emits electromagnetic radiation,for example, visible, infrared or ultraviolet light. The laser diode canbe positioned in the pocket and moved toward the waveguide until itabuts the stops 64 and 66. The stops prevent contact between the laseroutput facet and the waveguide input facet.

For the apparatus of FIG. 3, the alignment is achieved between theoutput facet of the laser and the input facet of the waveguide byplacing a laser diode in the pocket and pushing the laser diode forwardto the stops. The input facet on the waveguide side can be formed by avertical etch process and can be wider than the active output area(i.e., the output facet) of the laser diode. This design allows precisecontrol of the distance between the output facet of the laser diode andthe input facet of the waveguide. The distance 80 between the outputfacet of the laser diode and the input facet of the waveguide is definedby depth of the recess in the wall of the pocket. Thus the active areaof the laser diode is not in mechanical contact with the waveguide, andremains undamaged.

The relative position between the laser output facet and the waveguideinput facet in the lateral direction (i.e., the X direction) can becontrolled with an etched step in a wall of the pocket and one or morestops on the laser diode. This is shown in an embodiment illustrated inFIG. 4, wherein a portion of a slider 90 includes a waveguide 92 and apocket 94. In this example, the laser diode 96 includes one or morestops 98 and an overhanging portion 100. The stops on the laser diodeside could be projections positioned on opposite sides of the laseroutput facet 102. Alternatively, the stops could be portions of a sideof the laser diode, with the output facet being recessed in the side.With this structure, the distance between stops on the laser diode andthe output facet could be defined by a photolithography process. Thusthe geometrical distance control is the same as the precision of thephotolithography process, which could be below 50 nm.

A structure that provides for lateral alignment (i.e., in theZ-direction) is shown in FIG. 5. The structure includes one or moreetched grooves in the base of the pocket and a mesa structure on thelaser chip. In the embodiment of FIG. 5, a laser diode 110 includes alongitudinally extending mesa or projection 112 that fits within agroove 114 in the base or bottom of the pocket 116. The mesa could beused to define optical and current confinement for a single mode laserdiode. In this configuration, the central portion of the protruding mesacontains the active laser quantum well. The outer regions (that are usedfor mechanical referencing) are etched away down to the base substratematerial of the laser.

FIG. 6 is a schematic representation of a portion of a slider 120constructed in accordance with another embodiment. In the embodiment ofFIG. 6, alignment in the vertical direction (i.e., the Y direction) iscontrolled during a bonding process, in which the laser diode 122 ismounted in the slider pocket by a bonding compound 124. The sliderincludes etched stops 126 and 128 to provide vertical distance controlwithout precise control of bonding compound thickness. One way to get arepeatable vertical position of the laser diode chip is to hold it downduring the bonding process. Another approach to holding the laser chipis to use the bonding compound surface tension during bonding. Thisapproach can be considered to be a two-step process. The first step isto place the laser diode chip in the pocket with rough tolerance of 2-5microns. In the second step, surface tension force could be used toprecisely align the laser diode and channel waveguide as a result of areflow process using the bonding compound.

FIG. 7 shows an example of a portion of a slider 140 having a pocket 142with stops 144 and 146. The slider includes a planar waveguide portion148 having an input facet 150 adjacent to the pocket. The input facet isin a recess 152 in a wall 154 of the pocket, with stops 144 and 146 onopposite sides of the recess. A laser diode 156, which can be in theform of a laser chip, includes an output facet 158 from which the laseremits electromagnetic radiation, for example, visible, infrared orultraviolet light. The laser diode can be positioned in the pocket andmoved toward the waveguide until it abuts the stops 144 and 146. Thestops prevent contact between the laser output facet and the waveguideinput facet.

For the example of FIG. 7, the alignment is achieved between the outputfacet of the laser and the input facet of the waveguide by placing alaser diode in the pocket and pushing the laser diode forward to thestoppers. The input facet on the waveguide side can be formed by avertical etch process and can be wider than the active output area(i.e., the output facet) of the laser diode. This design allows precisecontrol of the distance between the output facet of the laser diode andthe input facet of the waveguide. More specifically, the distance 160between the output facet of the laser diode and the input facet of thewaveguide is defined by depth of the recess in the wall of the pocket.Thus the active area of the laser diode is not in mechanical contactwith the waveguide, and remains undamaged.

A plurality of solder bumps 162 are positioned on the bottom 164 of thepocket 142. A laser diode contact pad 164 is also positioned on thebottom of the pocket and could have shape presented in FIG. 7. Thecontact pad 166 on the bottom of the pocket serves as a heat sink. Thefinal laser diode chip position will depend on the location of wettingregions, the amount of bonding compound (eutectic) material between thebottom of the pocket and the laser diode, and the stop design. Thestructure of FIG. 7 can be used in flip chip bonding methods. Examplesof the bonding compound include solder and epoxy.

FIGS. 8-12 illustrate how the bonding process can be used to force thelaser diode toward the stops. FIG. 8 shows a cross-sectional view of aportion of the bottom of a pocket in a slider 170. A seed layer 172 ispositioned on the bottom of the pocket. A plurality of contact pads 174are positioned on the openings in insulator 174 above the seed layer.The contact pads are formed of a wettable “under bump metallurgy” (UBM)material (e.g., Au, Cu, Ni, Cr, Ti, TiW) that will allow the formationof a good solder bump. An insulating material 176 is positioned betweenthe contact pads. Contact pads may be used just for positioning or alsofor electrical contact.

FIG. 9 shows a cross-sectional view of the structure of FIG. 8, with theaddition of a plurality of bonding compound (e.g., eutectic material)bumps 178 on the contact pads 174.

FIG. 10 shows a cross-sectional view of the structure of FIG. 9, withthe addition of a laser diode 180 having a seed layer 182 on a bottomsurface, and a plurality of contact pads 184 positioned on the seedlayer. An insulating material 186 is positioned between the contactpads. The position of the contact pads on the laser diode is inherentlyoffset with respect to the contact pads in the pocket due to placementtolerances.

FIG. 11 shows self alignment due to a material reflow (e.g., solderreflow), wherein the laser diode is offset with respect to a desiredreference surface in the slider and surface tension of the reflowingeutectic material creates a force illustrated by arrow 188.

FIG. 12 shows a cross-sectional view of the structure of FIG. 11,following solidification of the eutectic material. From FIGS. 8-12, itcan be seen that surface tension forces of the bonding compound can beused to align the contact pads on the laser diode with the contact padsin the pocket. By selecting the relative position of the contacts padson the diode and the pocket, surface tension forces can be used to urgethe laser into contact with the stops in FIGS. 3 and 7. In addition, thebumps can be intentionally offset to drive the laser into the mechanicalstops before self-alignment equilibrium is reached.

In an embodiment, multiple laser chips can be simultaneously bonded tomultiple sliders. Precise alignment of the laser diode output facet andthe input facet of the channel waveguide is achieved by using laserdiode beds with specially designed features, like stops and steps.Placement of the laser diode is immediately followed by solder reflow ina single tool, so these two process steps described above effectivelybecome one production step. The method is illustrated in FIGS. 13-15.

FIG. 13 is a cross-sectional view of a first wafer 200 (also called ahead wafer) including a plurality of slider portions 202 and secondwafer 204 (also called a carrier wafer) including a plurality of laserdiodes 206. The slider portions include beds 208, each having aplurality of solder bumps 210. The carrier wafer includes a plurality ofopenings 212 that allow for the passage of hydrogen radicals from ahydrogen radical source 214. Each of the laser diodes also includes aplurality of solder bumps 216. When the two wafers are separated asshown in FIG. 13, the hydrogen radicals perform a cleaning function toclean the solder bumps. Hydrogen radicals can be formed using a processsuch as an atmospheric plasma. Alternatively, an active gas (such asformic acid) may be used to create preferential surface conditions onthe solder surface.

FIG. 14 shows the structure of FIG. 13, wherein the second wafer hasbeen moved toward the first wafer such that the solder bumps in the bedsand on the diodes merge. In the step illustrated in FIG. 14, surfacetension forces are used to urge the laser diodes toward stops thatdefine the eventual relative position of the laser diode output facetand the waveguide input facet.

FIG. 15 shows the structure of FIG. 14, wherein the carrier wafer hasbeen moved away from the first wafer, leaving the laser diodes attachedto the first wafer.

In one embodiment, an AlTiC head wafer is fabricated with waveguideelements and etched beds (or pockets) to receive the laser diodes. Thesepockets may include features for passive alignment, such as mechanicalstops and/or solder bumps. The etched pockets define the eventualposition of laser diode chips. The carrier wafer includes holes to allowthe flow of chemically active substances such as hydrogen radicalsand/or formic acid vapor. The size of the etched pockets should matchthe placing accuracy of a fast speed pick-and-place tool. The pocketposition matches the position of slider portions in the head wafer. Thesize of the carrier wafer could be the same or bigger than the headwafer.

The laser diodes can be placed into the pockets on the carrier waferwith the fast speed pick-and-place tool. The laser diodes initially liein pockets on the carrier wafer without mechanical attachment. Possiblelaser chip movements caused by vibration or incorrect horizontalorientation are limited by the carrier wafer pockets walls. Freemovement of laser chips could be used to reduce placement tool positionvariation by using the pocket walls as mechanical stoppers.

The source of a chemically active substance can have a size matching thecarrier wafer. An example of this source is a commercially availableatmospheric plasma tool.

The process of assembling the laser diodes and the sliders, asillustrated in FIGS. 13-15, includes the steps shown in the flowchart ofFIG. 17. First, the carrier wafer is positioned 230 into proximity ofthe head wafer, with a spacing, for example, of several millimeters (seeFIG. 13). The source is positioned 232 near the carrier wafer to providea flow of chemically active substance through the holes in the carrierwafer. The source is switched on 234 and the wafers are heated above thesolder melting point. Some time is allowed 236 for solder reflow andsolder surface pre-clean to remove oxide from solder surface. The gapbetween the wafers should be chosen to allow access to the solder onboth wafers by the cleaning substance at the same time.

Next, the wafers are brought into contact 238 so that solder on bothwafers touch each other (see also FIG. 14). The cleaning processcontinues immediately before bonding until the small gap restrictsaccess to the solder. In the case of passive alignment with mechanicalstops, additional movements may be applied 240 to push laser diode chipsinto contact with stops on the head wafer, and switch off the heater242. Continue to push 244 the lasers toward the stops during soldersolidification. After solidification, the carrier wafer is disengaged250 (see also FIG. 15). If using the solder bumps for self-alignment,the laser is allowed to float 246 and the heater is switched off 248.The lasers should be floating during solder solidification.

The bond pad geometry and layout has a significant effect on theself-alignment properties of the laser diode. Primarily, the size, shapeand volume of the solder array directly affect the alignmentcharacteristics. A nominal layout is shown in FIG. 16, which shows anexample of a self-alignment bond pad layout for an edge emitting laserdiode 220 with a central heat-sink connection 222 and outer alignmentpads 224. The pad layout includes a combination of solder self-alignmentbumps and an elongated heat sink connection to provide solderself-alignment, electrical contact, and thermal cooling through theslider/head structure.

While several embodiments have been described, it will be apparent tothose skilled in the art that various changes can be made to thedescribed embodiments without departing from the scope of the claims.The implementations described above and other implementations are withinthe scope of the following claims.

What is claimed is:
 1. A method comprising: positioning a carrier waferrelative to a head wafer such that each of a plurality of lasers of thecarrier wafer is aligned with an alignment feature of a correspondingone of a plurality of slider portions of the head wafer; injecting a gasbetween the carrier wafer and the head wafer via openings in at leastone the carrier wafer and the head wafer to create preferential surfaceconditions on solder surfaces therebetween; and performing a reflowoperation to bond the lasers to the corresponding slider portions,wherein the reflow operation further causes a final alignmenttherebetween in cooperation with the alignment features of the sliderportions.
 2. The method of claim 1, wherein the alignment featurefacilitates alignment between the lasers and channel waveguides of thecorresponding slider portions.
 3. The method of claim 2, wherein thealignment features comprise at least one of pockets on the sliderportions and mechanical stops between output facets of the lasers andinput facets of the channel waveguides, wherein the mechanical stopsseparates the input facets and output facets by a gap at least followingthe final alignment.
 4. The method of claim 1, wherein the reflowoperation further causes the final alignment in response to surfacetension of solder bumps between the lasers and the slider portions. 5.The method of claim 4, further comprising disengaging the carrier waferfrom the lasers during the reflow operation, thereby allowing the lasersto float during solder solidification following the reflow operation. 6.The method of claim 1, wherein positioning the carrier wave relative thehead wafer comprises leaving a spacing between the lasers and sliderportions, the method further comprising bringing the lasers into contactwith the slider portions during the reflow operation.
 7. The method ofclaim 1, wherein the gas comprises a hydrogen radical.
 8. The method ofclaim 1, wherein the gas comprises a surface activating gas.
 9. Themethod of claim 1, wherein each laser comprises an edge emitting laserdiode.
 10. The method of claim 1, further comprising, after the reflowoperation, moving the carrier wafer from the head wafer, leaving thelasers attached to the first wafer.
 11. The method of claim 1, furthercomprising, before positioning the carrier wafer relative to the headwafer, placing the lasers into pockets on the carrier wafer with a fastspeed pick-and-place tool.
 12. The method of claim 11, wherein the wallsof the pockets limit movement of the lasers caused by vibration orincorrect orientation.
 13. The method of claim 1, wherein each of theslider portions comprises a channel waveguide and a pocket having a walland a bottom, the bottom of the pocket adjoined with and at an angle tothe wall of the pocket, an input facet of the channel waveguide beingdisposed in a recess of the wall.
 14. The method of claim 13, whereinpositioning the carrier wafer relative to the head wafer comprises:positioning each laser at the bottom of each pocket outside of therecess such that an output facet of the laser directs light to the inputfacet in a lateral direction along the bottom of the pocket; and forcingeach laser along the bottom of each pocket in the lateral directionuntil each laser abuts the wall of each pocket such that the recess inthe wall of each pocket forms a gap between the output facet of eachlaser and the input facet of each channel waveguide in the lateraldirection.
 15. The method of claim 14, wherein forcing each laser towardthe wall of each pocket comprises using surface tension forces ofbonding material to push each laser toward the wall to align the outputfacet of the laser with the input facet of the channel waveguide. 16.The method of claim 15, wherein an intentional laser offset is used toallow lateral alignment to occur prior to contact with the wall.
 17. Themethod of claim 15, wherein the relative alignment between laser padsand substrate pads is offset such that contact between the laser and thewall in an axial direction is reached prior to full alignment.